io6 EXPERIMENTAL EVOLUTION LECT. 



instances might be given of man having muscles which 

 are considered as peculiar to the ape, horse, dog, 

 bear, &c. 1 



Variations also occur frequently in the anatomy of 

 many internal organs. Wallace refers to the 

 variability in the length of the digestive system in 

 the giraffe and other animals, and in the nature and 

 position of the gall-bladder, which in the same species 

 is sometimes present, either single or double, some- 

 times absent. These variations are not confined 

 to higher animals. Claus observes that ^Equorea 

 forskalea, a Ccelenterate, varies much in the number 

 of the radiating canals 2 ; and many botanists have 

 noticed the important structural variations which 

 obtain in plants. E. Mer has carried his investigations 

 into great detail in regard to Isoetes laciistris, and 

 other plants. 3 It results from these investigations 

 that the internal anatomy of plants may vary 

 considerably. This variability displays itself also in 

 regard to sex ; for it has been shown that external 

 influences play a large part in the determination 



1 Cf. R. Wiedersheim, Der Bail des Menschen ah Zeugniss seiner 

 Vergangcnheit (Freiburg i. B., 1880). 



2 American Naturalist, vol. xvi., 1882, p. 147. 



3 De F Influence exercee parle Milieu stir la Forme, la Structure, et le 

 Mode de Reproduction de F Isoetes lacustris. Ccmptes Rendus 1881, p. 

 94 (Jan.-July). See also Des Causes qui modifcnt la Strttcture de 

 ccrfaines Plantcs aquatiques vegetant dan F Eau. Bull. Soc. Botanique^ 

 1880, p. 194. 



